1. Field of the Invention
The invention relates to methods for manufacturing toothed gears and, more particularly, to a method for manufacturing bevel gears with reduced runout by using the gear tooth top lands as a datum.
2. Background of the Invention
The traditional methods for manufacturing bevel gears with shafts involves several steps. First, a rough forging or bar stock would be machined into a blank which would include center bores used as manufacturing location points, or datums. The blank could include threads or splines as needed, or threads or splines could be added at a later operation. After blanking, the gear teeth are cut into the workpiece.
Spiral bevel and hypoid gear pairs are conventionally produced utilizing either an intermittent index face milling method or a continuous indexing face hobbing method. Until recently, face milling of gear teeth was the preferred method. The face hobbing process has been recently adopted by some gear manufacturers, especially those gear manufacturers who make the spiral bevel and hypoid gear sets for vehicular applications. In a face hobbing machine, a circular face hob type rotary cutter carrying a plurality of cutter blades mounted in groups, is utilized, and a workpiece (gear blank) and the cutter continuously rotate in a timed relationship until the entire part is completed. During the cutting process, the workpiece indexes in a rotary manner so that each successive cutter blade groups engaging successive tooth slots as the gear or pinion member is being cut. The face hobbing method requires fewer production steps and less production time than the face milling method.
Normally, the tooth top lands of the gear teeth are not machined at the same time as the gear tooth profiles are cut, which incurs a great deal of eccentricity between a gear teeth pitch line and the top land. Surfaces such as centers had to be added to the gears, or expensive and complicated equipment such as gear pitch line chucks had to be purchased and maintained for machining the gears.
Thus, there is a need for an improved method for manufacturing bevel gears that overcomes shortcomings of the conventional independent drive axles.